1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices. More particularly, the present invention relates to a driving circuit of a backlight unit used in liquid crystal display (LCD) devices and a driving method using the same.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are advantageously light-weight, dimensionally compact, and consume a relatively low amount of power during operation. Consequently, LCD devices are widely used as displays in office automation and audio/video equipment.
Generally, LCD devices include an image display unit, e.g., LCD panel having a plurality of pixels arranged in a matrix pattern. When image signals are applied to the plurality of pixels, an orientation of liquid crystal molecules contained within the LCD device is altered. When the orientation of liquid crystal molecules is altered, the light transmittance characteristics of the plurality of pixels are manipulated and an image is displayed.
By themselves, LCD panels do not emit light. Therefore, a light source (e.g., a cold cathode fluorescent lamp or a light-emitting diode) must be used to express images formed at the LCD panel. Due to their low heat emission, high brightness, long life span, and full color display capabilities, cold cathode fluorescent lamps are widely used and preferred over light-emitting diodes as light sources suitable for use within LCD devices.
FIG. 1 illustrates a schematic view of an LCD device including a related art lamp-driving circuit.
Referring to FIG. 1, a lamp 130 emits light to an image display unit 140. The emitted light is then selectively transmitted by the image display unit 140 and an image is thus expressed. The lamp 130 emits light when AC power P is output from an inverter unit 120. The AC power P induces a tube current IL to flow within the lamp 130 and aid in the emission of light. Generally, the inverter unit 120 outputs the AC power P by boosting a low voltage direct current (DC) power output from a power source unit 110 into high voltage AC power P. Accordingly, the inverter unit 120 typically includes a switching element and a transformer.
FIG. 2 illustrates tube current and brightness of light emitted by a lamp versus time in the related art lamp-driving circuit.
Referring to FIG. 2, the tube current IL quickly increases as an input time, t, progresses until, at the end of a first time period t1, the tube current IL is saturated and maintained at a value of IL1 (i.e., 6 mA). While the brightness of light emitted by the lamp 130 is affected by the tube current IL, the brightness of light emitted by the lamp 130 slowly increases as the input time, t, progresses. Consequently, the brightness of light emitted by the lamp 130 increases after the tube current IL is saturated and maintained at the value of IL1 until, at the end of a second time period t2 (typically about five minutes), the brightness of light emitted by the lamp reaches an acceptable value, Y.
Because the related art lamp 130 attains the acceptable brightness value Y only after power P has been applied to the lamp 130 until the end of the second time period, t2, the quality with which images are displayed by the image display unit 140 is unsatisfactory until the end of the second time period, t2.